Patient table with integrated x-ray volumetric imager

ABSTRACT

Methods and apparatus for integrating a table with at least one X-ray source for medical imaging of patients. The apparatus comprises a table on which a patient may be placed, at least one X-ray source configured to generate X-rays at a plurality of X-ray source locations along a linear direction, wherein the at least one X-ray source is arranged to generate the X-rays such that at least some of the X-rays pass through a portion of the table in addition to passing through a portion of a patient placed on the table, and at least one detector array comprising a plurality of detector elements and arranged to detect the at least some of the X-rays passed through the portion of the patient placed on the table, wherein the at least one detector array comprises detector elements arranged in a two-dimensional configuration. Iterative reconstruction techniques may be used to reconstruct an image from X-ray data detected using the at least one detector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Application Serial No. 61/977,745 entitled “Patient Tablewith Integrated X-Ray Volumetric Imager” filed Apr. 10, 2014, underAttorney Docket No. L0632.70116US00, which is herein incorporated byreference in its entirety.

BACKGROUND

X-ray imaging technology has been employed in a wide range ofapplications from medical imaging to detection of unauthorized objectsor materials in baggage, cargo or other containers generally opaque tothe human eye. X-ray imaging typically includes passing high-energyradiation (i.e., X-rays) through an object to be imaged. X-rays from asource passing through the object interact with the internal structuresof the object and are altered according to various characteristics ofthe material (e.g., transmission, scattering and diffractioncharacteristics, etc.). By measuring changes (e.g., attenuation) in theX-ray radiation that exits the object, information related to materialthrough which the radiation passed may be obtained to form an image ofthe object.

In order to measure X-ray radiation penetrating an object to be imaged,an array of detectors responsive to X-ray radiation typically isarranged on one side of the object opposite a radiation source. Themagnitude of the radiation, measured by any detector in the array,represents the density of material along a ray from the X-ray source tothe X-ray detector. Measurements for multiple such rays passing throughgenerally parallel planes through the object can be grouped into aprojection image. Each such measurement represents a data point, or“pixel,” in the projection image.

Projection imaging is well suited for finding objects that have materialproperties or other characteristics such that they produce a group ofpixels having a recognizable outline regardless of the orientation ofthe object to be imaged. However, projection images are not well suitedfor reliably detecting or characterizing some objects. If the rays ofradiation pass through only a thin portion of the object or pass throughmultiple objects, there may be no group of pixels in the projectionimage that has characteristics significantly different from other pixelsin the image. The object may not be well characterized by, or even bedetected in, the resultant projection image.

Measuring attenuation of X-rays passing through an object from multipledifferent directions can provide more accurate detection of relativelythin objects. For instance, in a computed tomography (CT) scanner, suchmeasurements may be obtained by placing the X-ray source and detectorson a rotating gantry. As the gantry rotates around the object,measurements are made on rays of radiation passing through the objectfrom many different directions.

Multiple projection images can be used to construct a three-dimensional,or volumetric, image of the object. A volumetric image is organized inthree-dimensional sub-blocks called “voxels”—analogous to pixels in atwo-dimensional image—with each voxel corresponding to a density (orother material property) value of the object at a location inthree-dimensional space. Even relatively thin objects may form arecognizable group of voxels in such a volumetric image.

The process of using multiple radiation measurements from differentangles through an object to compute a volumetric image of the object isherein referred to as volumetric image reconstruction. The quality ofvolumetric image reconstruction not only depends on the geometry of theimaged object, but also on the geometry of the imaging system includingthe relative positions of X-ray sources and detectors used to make themeasurements. The relative positions of sources and detectors controlthe set of angles from which each voxel is irradiated by X-rays.

CT scanners have also found utility for medical applications where aportion of a patient may be scanned to determine the extent of an injuryor other medical condition. For example, a patient may be scanned usinga CT scanner prior to undergoing surgery to remove implanted foreignobjects as a result of an automobile accident, an explosion, or someother traumatic event. Reconstructing a volumetric image of the portionof the patient that will be operated on provides the surgeon withinformation about the foreign object(s) to help guide the surgicalintervention.

SUMMARY

The inventors have recognized and appreciated that some conventionalX-ray scanners have limited application in environments where rapid CTscans of patients would facilitate medical intervention. For example, insome military applications, it would be advantageous to perform CT scanson wounded soldiers on the battlefield to quickly assess injuries priorto performing surgery on such patients. However, some conventional CTscanners are large machines that are not portable or easilytransportable by a vehicle (e.g., a helicopter) to battlefields or othersimilar environments. Additionally, conventional CT scanners, whichtypically include X-ray sources and/or detectors located on a rotatinggantry, include moving parts that may not perform well in harsh physicalenvironments with varying degrees of temperature fluctuation and otherphysical impediments. Accordingly, some embodiments are directed tomethods and apparatus for rapidly obtaining X-ray images of a patientusing a portable X-ray imager integrated with a table (e.g., anoperating table, a surgical table, a stretcher, a litter, a gurney,etc.).

Although illustrative embodiments described in more detail below relateto deployment of embodiments for military applications (e.g., onbattlefields), it should be appreciated that embodiments of theinvention are not restricted based on any particular application. Forexample, some embodiments may be used in emergency applications (e.g.,on an ambulance, for search and rescue), in conventional medicalfacility environments (e.g., a surgical room of a hospital), orembodiments may be used for any other suitable application or with anyother suitable environment.

In one aspect, some embodiments are directed to an apparatus,comprising: a table on which a patient may be placed; at least one X-raysource configured to generate X-rays at a plurality of X-ray sourcelocations along a linear direction, wherein the at least one X-raysource is arranged to generate the X-rays such that at least some of theX-rays pass through a portion of the table in addition to passingthrough a portion of a patient placed on the table; and at least onedetector array comprising a plurality of detector elements and arrangedto detect the at least some of the X-rays passed through the portion ofthe patient placed on the table.

In another aspect, some embodiments are directed to a method ofmanufacturing an apparatus comprising a table on which a patient may beplaced; at least one X-ray source configured to generate X-rays at aplurality of X-ray source locations along a linear direction, whereinthe at least one X-ray source is arranged to generate the X-rays suchthat at least some of the X-rays pass through a portion of the table inaddition to passing through a portion of a patient placed on the table;and at least one detector array comprising a plurality of detectorelements and arranged to detect the at least some of the X-rays passedthrough the portion of the patient placed on the table.

In another aspect, some embodiments are directed to a method ofvolumetric image reconstruction comprising: receiving X-ray data from atleast one detector array, wherein the received X-ray data does notsatisfy a volumetric reconstruction requirement; and reconstructing,with at least one computer processor, the volumetric image using aniterative reconstruction technique based, at least in part, on thereceived data.

In another aspect, some embodiments are directed to a non-transitorycomputer readable medium encoded with a plurality of instructions that,when executed by at least one computer processor perform a method. Themethod comprises receiving X-ray data from at least one detector array,wherein the received X-ray data does not satisfy a volumetricreconstruction requirement; and reconstructing, with the at least onecomputer processor, the volumetric image using an iterativereconstruction technique based, at least in part, on the received data.

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below (provided thatsuch concepts are not mutually inconsistent) are contemplated as beingpart of the inventive subject matter disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic of an illustrative imaging apparatus in accordancewith some embodiments;

FIG. 2 is a sketch illustrating aspects of forming a multiviewvolumetric image, in accordance with some embodiments;

FIG. 3 is a schematic of an illustrative surgical table that may be usedin accordance with some embodiments; and

FIG. 4 is an illustrative process for reconstructing a volumetric imagein accordance with some embodiments.

DETAILED DESCRIPTION

Challenging environmental conditions, such as military battlefields orforward medical stations provide unique challenges that are not wellsuited for imaging injured patients using conventional CT scanners. Forexample, it is very difficult to obtain timely CT scans for diagnosis orsurgical guidance on injured soldiers in emergency situations.Accordingly, some embodiments of the invention are directed torapid-acquisition, in-situ, field-robust, portable X-ray imaging methodsand apparatuses that are practical for use in such challengingenvironments.

Some embodiments of the invention are directed to an X-ray apparatusintegrated with a table on which a patient may be placed. The table maybe a surgical table on which the patient is placed for a surgicalprocedure, such as removal of one or more bullets from a gunshot wound,removal of one or more pieces of shrapnel from a battlefield injury,etc. A limitation of some conventional CT scanners is that they may notbe closely integrated with surgical tables, such that repeated imagingof a patient cannot be performed during a surgical procedure withoutsubstantial adjustment of the CT scanner and/or the patient between eachimaging session. For example, conventional tomosynthetic C-arm scannerstypically require repositioning and/or repositioning of the patientprior to the imaging session and following the imaging session tocontinue the surgical procedure. Additionally, conventional CT scannerswhen used during a surgical procedure, typically obstruct a surgeon orother medical professional from accessing the patient on the tableduring the imaging session. Accordingly, some embodiments are directedto an X-ray apparatus integrated with a surgical table that does notobstruct a physician from accessing a patient during and/or immediatelyfollowing an imaging session. Other advantages of embodiments of theinvention are apparent from the discussion following below.

FIG. 1 shows an imaging apparatus 100 in accordance with someembodiments of the invention. Imaging apparatus 100 includes table 110on which a patient 116 may be placed. In some embodiments table 110 maybe a surgical table having standard dimensions of 76″×20″×30″ or anyother suitable dimensions. FIG. 3 shows a schematic of an illustrativesurgical table 310 with exemplary dimensions shown in millimeters.

Table 110 may be made of any suitable material including, but notlimited to, steel, carbon fiber, fabric, cloth, canvas, and wood. Atleast a portion of table 110 may be made of a material that enablesX-rays to pass through the at least a portion of the table. For example,in some embodiments, at least a portion of table 110 may comprise carbonfiber material that forms a window 114 through which X-rays generated byat least one X-ray source may pass. In some embodiments, table 110 maybe implemented as a removable litter, gurney, or stretcher, and the atleast one window 114 in table 110 may comprise canvas, fabric, cloth,wood, or any other suitable material that enables X-rays to pass throughthe at least one window. In some embodiments, at least one window in theX-ray table may be devoid of material such that X-rays generated by atleast one X-ray source may pass through the at least one window thatdoes not include any material. The at least one window in table 110 maybe any suitable size including, but not limited to, the size of theentire table surface.

In some embodiments, at least a portion of table 110 may be movable suchthat the at least a portion of the table may translate in one or moredirections to enable different portions of a patient placed on the tableto be in the path of X-rays generated by at least one X-ray source.Translation of table 110 may achieved in any suitable way. For example,some embodiments may include one or more rails that enable at least aportion of the table to be translated in the length direction and/or thewidth direction of the table. In other embodiments, table 110 may bestationary, and at least one X-ray source used to image a patient may bemovable, for example, along one or more rails attached to the table.

Imaging apparatus 100 also includes X-ray source 112 configured togenerate X-ray radiation 118 that passes through at least a portion oftable 110. In some embodiments, X-ray source 112 is a linear X-raysource configured to generate X-rays at a plurality of X-ray sourcelocations along a linear direction. In some embodiments, X-ray source112 is a stationary X-ray source that generates X-ray radiation at aseries of time-multiplexed spatial locations passing through table 110without requiring any moving parts (e.g., without requiring a rotatablegantry). A stationary source, as that term is used herein, is a sourcethat does not move during a single acquisition of an image. Suchstationary sources may be electronically-controlled, such that X-rayenergy may be generated at different spatial locations. An example ofsuch a stationary X-ray source is an e-beam. In e-beam imaging systems,one or more e-beams are directed to impinge on the surface of a targetresponsive to the e-beams. The target may be formed from, for example,tungsten, molybdenum, gold, or other material that emits X-rays inresponse to an electron beam impinging on its surface. For example, thetarget may be a material that converts energy in the e-beam into X-rayphotons, emitted from the target essentially in the 4π directions. Thereleased energy may be shaped or collimated by blocking selectedportions of the X-rays emitted from the target using any of variousradiation absorbing material (such as lead). For example, the X-ray maybe collimated to form a cone beam, a fan beam, a pencil beam or anyother X-ray beam having generally desired characteristics. Thecollimated X-rays may then pass into an inspection region to penetratean object of interest to ascertain one or more characteristics of theobject.

While conventional X-ray scanning systems employ one or more sources anddetectors positioned or rotated in a circular geometry, e-beam imagingsystems may comprise arbitrary, and more particularly, non-circulargeometries, which offers a number of benefits with respect to theflexibility of the design and may facilitate more compact andinexpensive X-ray detection system. In an exemplary X-ray scanningsystem, the target which converts energy in an e-beam to X-ray energymay be provided as one or more linear segments.

Additionally, different types of stationary sources may be used invarious embodiments of the invention. For example, in oneimplementation, X-ray source 112 may comprise a plurality of carbonnanotube elements that each act as an individual source activated byapplying in time-sequence a signal to each of the elements. An X-raysource comprising a plurality of carbon nanotube elements may also beconfigured as a linear source in accordance with the techniquesdescribed herein.

In other embodiments, X-ray source 112 may comprise a distributed arrayof switchable X-ray sources that, when activated in time-sequence, emitX-ray radiation. The switchable X-ray sources in the distributed arraymay be activated by application of any suitable signal to each sourceincluding, but not limited to, a voltage and a light source.

In other embodiments, X-ray source 112 may comprise a multi-energy X-raysource that emits X-ray radiation at more than one energy level. Forexample, the inspection system may include one or more X-ray generationsubsystems adapted to generate X-ray radiation at a first energy leveland a second energy level. Alternatively, a multi-energy X-ray sourcemay emit X-ray radiation at more than two energy levels. To supportmulti-energy imaging, each X-ray generation subsystem may generateradiation of a different energy level during successive intervals whenit operates. By correlating detector outputs to times in which the X-raygeneration subsystems are generating, for example, high-and low-energyX-rays, high and low X-ray data may be collected for a multi-energyimage analysis. Such an analysis may be performed using techniques asknown in the art or in any other suitable way.

X-ray source 112 may be integrated with table 110 in any suitable way.In some embodiments, X-ray source 112 may be mounted substantially belowtable 110. In such a configuration, X-rays generated from the X-raysource pass upward through table 110 and are detected by at least onedetector array 120 mounted above table 110, as discussed in furtherdetail below. In some embodiments, X-ray source may be mounted entirelybelow table 110, as shown in FIG. 1. In other embodiments, at least aportion of X-ray source 112 may extend at least partially above table110. For example, X-ray source 112 may include an portion that enablesX-rays to be generated in a direction perpendicular to the bottomsurface of table 110 (i.e., along the length direction and/or the widthdimension of the table). In some embodiments, the portion of X-raysource 112 extending above table 110 may be adjustable such that in afirst configuration the X-ray source is disposed entirely below thetable and in a second configuration the portion of the X-ray source isextended above the table. In embodiments in which at least a portion ofX-ray source 112 is mounted below table 110, at least some X-raysgenerated by X-ray source 112 pass through at least a portion of thetable prior to passing through a patient placed on the table.

As discussed above, in some embodiments X-ray source 112 may be movablerelative to at least a portion of table 110 to enable different portionsof a patient placed on table 110 to be imaged without moving the patienton the table. Any suitable mechanism may be used to enable X-ray source112 to be translated along the length dimension and/or the widthdimension of table 110 including, but not limited to, using one or morerails on which the X-ray source 112 and/or at least a portion of table110 may move.

Although X-ray source 112 is shown as being mounted below table 110, itshould be appreciated that in some embodiments, X-ray source 112 mayalternatively be mounted above table 110 and configured to generateX-ray radiation downward through the top surface of table 110. In suchan embodiment, at least one detector array may be integrated as aportion of the table 110 or mounted below table 110 to detect radiationpassing through the table.

Imaging apparatus 100 also includes detector array 120 comprising aplurality of detector elements and arranged to detect X-rays passedthrough the portion of the table 110 from X-ray source 112. Detectorarray 120 may include any suitable type of detectors for detectingX-rays, and the detectors may be arranged in any suitabletwo-dimensional configuration. In some embodiments, detector array 120comprises a flat panel detector array, as shown in FIG. 1. In someembodiments, detector array 120 may comprise a plurality of lineararrays of detectors arranged in a two-dimensional configuration. Inother embodiments, detector array 120 comprises a photodiode array withscintillator elements. In some embodiments, detector array 120 mayinclude one or more detector arrays mounted to a movable structure.Mounting the detector array 120 to a movable structure may enable thedetector array to be translated over a patient placed on the table toimage different parts of the body. Alternatively, mounting the detectorarray 120 to a movable structure may enable the detector array to bemoved out of the way during a medical procedure.

In embodiments employing a multi-energy X-ray source, at least some ofthe detectors in detector array 120 may be configured to classifyreceived X-ray radiation as having one of a plurality of energies, suchas a first energy or a second energy. For example, some or all of thedetectors in detector array 120 may be adapted to record individualX-ray photon arrival energies with sufficient resolution to separatephotons having a first energy from photons having a second energy. Thedetectors may be configured to classify the energy of received X-rayradiation by, for example, being constructed of a material, such asCdZnTe (CZT) that enables the classification of individual photons. Suchdetectors are known in the art and are often commonly referred to asphoton-counting detectors or multispectral detectors.

In some embodiments, detector array 120 may be mounted above table 110as shown in FIG. 1. Detector array 120 may be mounted in any suitableway including, but not limited to, mounting the detector array to avehicle such as a land, air, or sea-based military vehicle, ahelicopter, an ambulance, or an airplane. For example in someembodiments detector array 120 is mounted to a military vehicle, such asa sea vessel that cannot accommodate a conventional CT systems due tophysical size constraints of the ship/sea vessel and the form factor ofthe CT system (e.g., conventional CT systems may not fit through thehatches in such vessels).

As discussed above, some embodiments enable an integrated medical X-rayscanner to be portable, such that the X-ray scanner can be transportedfor military and/or emergency applications for which conventional X-rayscanners are incompatible. Some embodiments are of such a weight thatthey are helicopter-transportable. For example, imaging apparatusmanufactured in accordance with some embodiments may be less than tenthousand pounds, less than eight thousand pounds, less than fivethousand pounds, or less than two thousand pounds. Other embodiments areof a size that they are transportable in a vehicle such as an ambulance.To achieve such a size, some embodiments may include a compact X-raysource configured to fit entirely or substantially entirely within thedimensions of a conventional size ambulance gurney or table.

Conventional CT systems having a large contiguous structure, whereseveral components of the CT system including the X-ray source and thedetector array, are mounted on rotating gantry, have limited portabilityand configurability due to their size and form factor. In someembodiments, one or more components of the X-ray scanner are provided(e.g., manufactured) as modules that may be separately transported to alocation where the X-ray scanner is to be assembled, and the modularpieces of the system may be assembled at the desired location. Forexample, in some embodiments, one or more of an X-ray source, a detectorarray, a power source, and other electronics of the X-ray system may beprovided as separate modules that may be assembled into a an X-raysystem for generating X-ray-based images (e.g., CT images). Themodularity of such embodiments contributes to the portability of theX-ray system

Rather than being deployed in military or emergency vehicles or vessels,X-ray scanners in accordance with some embodiments may be installed intraditional medical facilities such as hospitals. In such applications,detector array 120 may be mounted to the ceiling of an operating room orother room at the medical facility. When mounted to the ceiling,detector array 120 may be fixed to the ceiling or mounted on a movablestructure that can be brought closer to the patient during imaging.Mounting detector array 120 on a movable structure may enable thedetector array to be reduced in size compared to mounting the detectorarray to the ceiling in a fixed configuration. In some embodiments,detector array 120 may alternatively be mounted on a movable or fixedstructure rather than being mounted on the ceiling of a vehicle orstructure.

In some embodiments, detector array 120 is associated with read-outcircuitry configured to read out information from the detector elementsof the detector array. The read out circuitry may be configured tosimultaneously read out information from all detector elements of thedetector array or a subset (i.e., less than all) of the detectorelements of the detector array. Information read out from the detectorelements of the detector array may be provided to at least one computerto perform a volumetric image reconstruction based on the read outinformation, as discussed in more detail below.

Imaging apparatus 100 also includes a computer 130 including at leastone processor programmed to reconstruct a volumetric image based, atleast in part, on X-rays detected by detector array 120. In someembodiments, computer 130 may be integrated with imaging apparatus 100as shown in FIG. 1. In other embodiments, computer 130 may be locatedremote from imaging apparatus 100 and X-ray data output from detectorarray 120 may be transmitted to the remotely-located computer 130 forimage reconstruction and/or analysis. For example, in a militaryapplication where a patient is imaged on the front lines of abattlefield by imaging apparatus 100, X-ray data output from detectorarray 120 may be transmitted to a computer 130 located in a saferlocation where a physician can analyze the images being reconstructedbased on the collected detector data. Alternatively, when computer 130is integrated with imaging apparatus 100, the image can be reconstructedusing computer 130, and the reconstructed image may be transmitted to aremotely-located computer for analysis, as embodiments of the inventionare not limited in the particular arrangement or location of computer130.

FIG. 2 is a sketch demonstrating aspects of computing a volumetric imagefrom measurements made on an object 200 (e.g., a region of the patient'sbody). In the simple example of FIG. 2, the imaged object 200 is dividedinto nine regions. An image of the object 200 is formed by computing aproperty of the material in each of these nine regions. Each of the nineregions will correspond to a voxel in the computed image. For thisreason the regions in the object are sometimes also referred to as“voxels.” In the simple example of FIG. 2, object 200 is divided intonine voxels of which V(1,1,1), V(1,1,2), V(1,1,3), V(2,2,3) and V(3,3,3)are numbered. To form a volumetric image of object 200, a materialproperty is computed for each of the voxels from the measured outputs ofdetectors, of which detectors 230 ₁, 230 ₂ and 230₃ are shown. In theillustrated embodiment, the material property is an average density ofthe material within the voxel.

In the embodiment illustrated, measurements from which density may becomputed are made by passing rays of radiation through the object 200from different directions. By measuring the intensity of the rays afterthey have passed through the object and comparing the measured intensityto incident intensity, attenuation along the path of the ray may bedetermined. If attenuation along a sufficient number of rays travelingin a sufficient number of directions is measured, the data collected canbe processed to compute the density within each of the voxelsindividually.

For example, FIG. 2 shows a source 220 ₁ and a detector 230 ₁. A raytraveling from source 220 ₁ to detector 230 ₁ passes through voxelsV(1,1,3), V(2,2,3) and V(3,3,3). As a result, the value measured atdetector 230 ₁ will depend on the densities in each of those voxels.Thus, the measurement taken at detector 230 ₁ of a ray from source 220 ₁may be used to estimate the density at each of the voxels V(1,1,3),V(2,2,3) and V(3,3,3).

As shown, a ray from source 220 ₁ to detector 230 ₁ represents just oneof the rays passing through object 200. Other rays are shown in theexample of FIG. 2. For example, a ray is shown passing from source 220 ₂to detector 230 ₂. As with the ray passing from source 220 ₁ to detector230 ₁, the value measured at detector 230 ₂ will depend on the densitiesof voxels V(1,1,3), V(2,2,3) and V(3,2,3) because the ray source 220 ₂passes through these voxels before impinging on detector 230 ₂.Similarly, the value measured at detector 230 ₃, with respect to a raypassing from passing from source 220 ₃ to detector 230 ₃, is influencedby the densities of the voxels along that ray (V(1,1,1), V(1,1,2), andV(1,1,3)).

FIG. 2 shows only three rays passing through object 200. Each of therays generates a single measurement representative of the densities ofvoxels, through which the ray passes, in object 200. In the simpleproblem illustrated in FIG. 2, object 200 is divided into 27 voxels.Accordingly, though FIG. 2 shows only three rays passing through object200, to compute a volumetric image of object 200, more measurements aretypically needed.

In a physical system, the number of measurements taken often exceeds thenumber of voxels in the image. For instance, measurements may be madesuch that multiple rays pass through each voxel with some of the rayspassing through each voxel from a range of angles. The range of anglesmay be any suitable range. For example, it may be desirable to have rayspassing through the object from a range of angles that exceeds 180°, ora range of angles that is as close to 180° as possible. Though in otherscenarios the range of angles may be smaller, for instance a range suchas 170°, 160°, 150°, or 140°, or even less may be used.

The inventors have recognized and appreciated that in certainimplementations (e.g., military and portable emergency implementations)acquiring rapid images may be as important or more important thanobtaining high quality images. Accordingly, in some embodiments, avolumetric image is reconstructed that includes some imaging artifacts.For example, the volumetric image may be reconstructed using informationthat does not satisfy one or more volumetric reconstruction requirement.Any suitable volumetric reconstruction requirement may be usedincluding, but not limited to a Tuy condition, a pi-line-condition, aNyquist condition, and a non-truncation condition. Additionally, in someembodiments a volumetric imaging reconstruction may be performed usinginformation corresponding to a range of angles substantially less than180°. In some embodiments, a controller may be provided to controloperation of the X-ray source(s) to achieve any desired range of anglesincluding a range of angles less than 180°.

Measurements obtained from multiple rays passing through the objectunder inspection may be used to compute a volumetric image. Forinstance, if a sufficient number of measurements along rays from asufficient number of independent angles are made, the measured outputsof the detectors may be used to define a system of simultaneousequations that, using an iterative mathematical technique, may be solvedfor the unknown values representing the densities of the individualvoxels in object 200.

Uncertainty or other variations in the measurement process may prevent asingle solution from satisfying simultaneously all equations in a systemof equations formed from the measurements. Thus, solving the system ofequations formed from actual measurements would involve finding thevalues that best solve the equations. Similarly, obtaining measurementsfrom multiple angles will allow voxels to be computed using a directmethod.

In some embodiments, an iterative reconstruction technique is used toreconstruct a volumetric image of an object. Any suitable iterativereconstruction technique may be used, and embodiments of the inventionare not limited in this respect. An example of an iterative method,termed the algebraic reconstruction technique (ART) computes a value ρfor each of the voxels in the imaged object. A maximum likelihoodestimate M² is defined as:

${{M^{2}\left( {\hat{\rho}}_{k} \right)} = {\sum\limits_{i}\; \frac{\left( {{X_{i}\left( {\hat{\rho}}_{k} \right)} - x_{i}} \right)^{2}}{\sigma_{i}^{2}}}},$

where X_(i) relates density at voxels through which a ray passes to ameasured value of the ray that has passed through the object. Estimatedvoxel densities {circumflex over (P)}_(k) are multiplied by X_(i), whichyields an estimate of values measured along the ith ray. By subtractingthis estimate from the actual measured value x_(i), an error value isobtained. When these error values are weighted by an uncertainty valueσ_(i), squared and summed with similarly computed values along otherrays, a value of M² results. The iterative technique aims to finddensity values ρ that minimize the changes in M² with respect to changesin density values. Density values that satisfy this criterion representthe computed image.

ART is only one many iterative reconstruction methods known in the art.Any of numerous iterative reconstruction techniques may be used insteadof or in addition to ART. For instance, any of the following techniquesmay be used: ordered-subsets simultaneous iterative reconstructiontechnique (OSIRT), simultaneous algebraic reconstruction technique(SART), simultaneous iterative reconstruction technique (SIRT),multiplicative algebraic reconstruction technique (MART), simultaneousmultiplicative algebraic reconstruction technique (SMART), least-squaresQR method, expectation maximization (EM), ordered subsets expectationmaximization (OSEM), convex method (C), and ordered-subsets convexmethod (OSC).

The inventors have appreciated that the use of iterative reconstructionmethods allows for rapid reconstruction of images based on X-ray datacollected using some embodiments of the invention. In some embodiments,an image reconstruction technique may be reconstructed using aregulator, which enables the reconstruction technique to select fromamong several possible image solutions. Any suitable regulator may beused, and embodiments of the invention are not limited in this respect.Illustrative regulators include, but are not limited to, a Tikhonovregulator, a total variation (TV) regulator, a Laplacian regulator, anda compressive sensing regulator.

In some embodiments, image reconstruction may be based, at least inpart, on image priors that constrain the image reconstruction space. Anysuitable image priors may be used, and embodiments of the invention arenot limited in this respect. For example, in some embodiments imagepriors may be determined based, at least in part, on at least onewhole-image statistics (e.g., k-means, k-nearest neighbor). In someembodiments, the at least one whole-image statistic may be based, atleast in part, on one or more images of the patient from a previousimaging session. In some embodiments, image priors may be determinedbased, at least in part, on a plurality of images obtained from aplurality of patients, and the image priors may be used to constrainimage reconstruction. For example, the plurality of images may be usedto identify a set of anatomical landmarks for a particular object to beimaged (e.g., a brain, a heart, a liver, etc.), and the anatomicallandmarks may be used as image priors in the image reconstruction. Itshould be appreciated that the plurality of images may alternatively beused in any other suitable way to determine image priors for imagereconstruction in accordance with some embodiments of the invention.

An imaging system constructed in accordance with one or more of thetechniques described herein may achieve an image reconstruction time fora volumetric image of acceptable image quality in substantially lesstime achievable using conventional CT scanners. For example, in someembodiments, a volumetric image may be reconstructed in less than oneminute. In some embodiments, a volumetric image may be reconstructed inless than thirty seconds. In some embodiments, a volumetric image may bereconstructed in less than five seconds.

FIG. 4 shows an illustrative process for reconstructing a volumetricimage based, at least in part, on X-ray data detected using someembodiments of the invention. In act 410, X-ray data is received from atleast one detector array. As discussed above, the received X-ray datamay correspond to data that has been collected using a range of X-rayangles substantially less than 180°, which is typically required forhigh-quality images taken using conventional CT scanners. The processproceeds to act 420, where the received X-ray data is used toreconstruct a volumetric image using one or more iterativereconstruction techniques, as described above. Following reconstruction,the process proceeds to act 430, where the reconstructed image isoutput. For example, the reconstructed image may be displayed on ascreen or data describing the reconstructed image may be transmitted toanother device for subsequent display and/or analysis.

Imaging apparatuses manufactured in accordance with some embodiments ofthe invention may include additional hardware and/or software componentsthat facilitate use of the imaging apparatus in particular applications.For example, in some embodiments, an imaging apparatus may include ashielding structure configured to at least partially shield a person(e.g., a surgeon) other than the patient being imaged from the X-raysgenerated by the X-ray source. Any suitable shielding structure may beused, and embodiments of the invention are not limited in this respect.For example, a portable shielding structure may be temporarily placedbetween the surgeon and the patient such that the surgeon can performmedical operations on the patient during or immediately prior toirradiating the patient with X-ray radiation for imaging. Alternatively,the surgeon or other medical professional may wear a shielding structureas a protective garment or vest to shield the surgeon from X-rayradiation. Any other suitable shielding structure (including noshielding structure) may alternatively be used.

As discussed above, a limitation of some conventional CT scanners usedin surgical environments is that imaging and performing medicalprocedures on a patient cannot be conducted simultaneously or nearsimultaneously because conventional CT scanners typically obstruct aphysician's access to the patient while the CT scanner is positioned forimaging. Proper positioning of conventional CT scanners typically takesa substantial amount of time, which is compounded if multiple imagingsessions are necessary. Imaging apparatus in accordance with someembodiments are designed to enable a person (e.g., a surgeon) to performat least one medical procedure on a patient placed on the table withouthaving to move the X-ray source or the detector array. For example, byintegrating the X-ray source with the table, and having a stationarydetector array, only minimal (or no) changes to imaging configurationneed be made to enable rapid and/or repeated imaging of a portion of aperson during a medical procedures. By enabling rapid and frequentimaging sessions to be achieved, some embodiments of the invention maybe better suited than conventional CT scanners in various environmentsincluding, but not limited to, military and emergency environments. Forexample, the use of rapid imaging may enable less or no sedation of theimaged patient and/or no movement of the patient on/off a surgical tablefor surgery.

As should be appreciated from the foregoing, X-ray imaging systemsdesigned according to the principles described herein, may produce aneconomical, fast and accurate images for medical applications whereimaging speed and portability are important or desired.

Additionally, imaging system manufactured in accordance with someembodiments of the invention may be “ruggedized” for use in harshenvironments using one or more temperature-insensitive components and/orby not including moving parts that are susceptible to failure in suchenvironments. Some embodiments may additionally or alternatively beruggedized by sealing one or more components of the imaging apparatus toprevent foreign debris from entering portions of the apparatus, orembodiments may be ruggedized using any other suitable technique ortechniques.

Alterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

The above-described embodiments of the present invention can beimplemented in any of numerous ways. For example, the embodiments may beimplemented using hardware, software or a combination thereof. Whenimplemented in software, the software code can be executed on anysuitable processor or collection of processors, whether provided in asingle computer or distributed among multiple computers.

Further, it should be appreciated that a computer may be embodied in anyof a number of forms, such as a rack-mounted computer, a desktopcomputer, a laptop computer, or a tablet computer.

Also, a computer may have one or more input and output devices. Thesedevices can be used, among other things, to present a user interface.Examples of output devices that can be used to provide a user interfaceinclude printers or display screens for visual presentation of outputand speakers or other sound generating devices for audible presentationof output. Examples of input devices that can be used for a userinterface including keyboards, and pointing devices, such as mice, touchpads, and digitizing tables. As another example, a computer may receiveinput information through speech recognition or in other audible format.

Such computers may be interconnected by one or more networks in anysuitable form, including as a local area network or a wide area network,such as an enterprise network or the Internet. Such networks may bebased on any suitable technology and may operate according to anysuitable protocol and may include wireless networks, wired networks orfiber optic networks.

Also, the various methods or processes outlined herein may be coded assoftware that is executable on one or more processors that employ anyone of a variety of operating systems or platforms. Additionally, suchsoftware may be written using any of a number of suitable programminglanguages and/or conventional programming or scripting tools, and alsomay be compiled as executable machine language code or intermediate codethat is executed on a framework or virtual machine.

In this respect, the invention may be embodied as a computer readablemedium (or multiple computer readable media) (e.g., a computer memory,one or more floppy discs, compact discs, optical discs, magnetic tapes,flash memories, circuit configurations in Field Programmable Gate Arraysor other semiconductor devices, etc.) encoded with one or more programsthat, when executed on one or more computers or other processors,perform methods that implement the various embodiments of the inventiondiscussed above. The computer readable medium or media can betransportable, such that the program or programs stored thereon can beloaded onto one or more different computers or other processors toimplement various aspects of the present invention as discussed above.By way of example, and not limitation, computer readable media maycomprise computer storage media. Computer storage media includes bothvolatile and nonvolatile, removable and non-removable media implementedin any method or technology for storage of information such as computerreadable instructions, data structures, program modules or other data.Computer storage media includes, but is not limited to, RAM, ROM,EEPROM, flash memory or other memory technology, CD-ROM, digitalversatile disks (DVD) or other optical disk storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other medium which can be used to store the desired informationand which can be accessed by a computer.

The terms “program” or “software” are used herein in a generic sense torefer to any type of computer code or set of computer-executableinstructions that can be employed to program a computer or otherprocessor to implement various aspects of the present invention asdiscussed above. Additionally, it should be appreciated that accordingto one aspect of this embodiment, one or more computer programs thatwhen executed perform methods of the present invention need not resideon a single computer or processor, but may be distributed in a modularfashion amongst a number of different computers or processors toimplement various aspects of the present invention.

Computer-executable instructions may be in many forms, such as programmodules, executed by one or more computers or other devices. Generally,program modules include routines, programs, objects, components, datastructures, etc. that perform particular tasks or implement particularabstract data types. Typically the functionality of the program modulesmay be combined or distributed as desired in various embodiments.

The invention may be embodied as a method, of which an example has beenprovided. The acts performed as part of the method may be ordered in anysuitable way. Accordingly, embodiments may be constructed in which actsare performed in an order different than illustrated, which may includeperforming some acts simultaneously, even though shown as sequentialacts in illustrative embodiments.

Various aspects of the present invention may be used alone, incombination, or in a variety of arrangements not specifically discussedin the embodiments described in the foregoing and is therefore notlimited in its application to the details and arrangement of componentsset forth in the foregoing description or illustrated in the drawings.For example, aspects described in one embodiment may be combined in anymanner with aspects described in other embodiments.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

What is claimed is:
 1. An apparatus, comprising: a table on which apatient may be placed; at least one X-ray source configured to generateX-rays at a plurality of X-ray source locations along a lineardirection, wherein the at least one X-ray source is arranged to generatethe X-rays such that at least some of the X-rays pass through a portionof the table in addition to passing through a portion of a patientplaced on the table; and at least one detector array comprising aplurality of detector elements and arranged to detect the at least someof the X-rays passed through the portion of the patient placed on thetable, wherein the at least one detector array comprises detectorelements arranged in a two-dimensional configuration.
 2. (canceled) 3.The apparatus of claim 1, wherein the table includes at least one windowthat enables the at least some of the X-rays to pass through the atleast one window.
 4. (canceled)
 5. (canceled)
 6. The apparatus of claim1, wherein the at least one X-ray source is mounted substantially belowthe table.
 7. The apparatus of claim 6, wherein the at least one X-raysource includes a portion that extends at least partially above thetable.
 8. (canceled)
 9. The apparatus of claim 1, wherein the at leastone X-ray source is mounted substantially above the table.
 10. Theapparatus of claim 1, wherein the at least one X-ray source isconfigured to be stationary during a single acquisition of data used toreconstruct an image.
 11. The apparatus of claim 1, wherein the at leastone X-ray source is mounted such that the at least one X-ray source istranslatable along a length direction and/or a width direction of thetable.
 12. The apparatus of claim 1, wherein the at least one sourcecomprises at least one e-beam source. 13-15. (canceled)
 16. Theapparatus of claim 1, wherein the at least one source comprises aplurality of sub-sources configured to be activated usingtime-multiplexing.
 17. The apparatus of claim 1, wherein the at leastone detector array comprises a flat-panel detector array.
 18. Theapparatus of claim 1, wherein the at least one detector array is mountedto a movable structure. 19-21. (canceled)
 22. The apparatus of claim 1,further comprising: at least one processor programmed with instructionsthat, when executed by the at least one processor, reconstruct avolumetric image based, at least in part, on the X-rays detected by theat least one detector array. 23-32. (canceled)
 33. The apparatus ofclaim 22, wherein reconstructing a volumetric image comprisesreconstructing a volumetric image using information that does notsatisfy a volumetric reconstruction requirement.
 34. (canceled)
 35. Theapparatus of claim 1, further comprising: a shielding structureconfigured to at least partially shield a person other than the patientfrom the X-rays generated by the at least one X-ray source.
 36. Theapparatus of claim 1, further comprising: read-out circuitry configuredto read out information from one or more detector elements of the atleast one detector array, wherein the read-out circuitry is configuredto provide the information read out from the one or more detectorelements to at least one processor programmed to perform a volumetricimage reconstruction.
 37. (canceled)
 38. (canceled)
 39. The apparatus ofclaim 1, wherein the at least one source and the at least one detectorare arranged to enable a person to perform at least one procedure on thepatient without moving the at least one source or the at least onedetector array.
 40. The apparatus of claim 1, wherein the at least onesource and the at least one detector are arranged to enable a person toperform at least one procedure on the patient during generation of theX-rays by the at least one X-ray source.
 41. The apparatus of claim 1,further comprising: a controller programmed to control operation of theat least one source, wherein the controller is programmed to control theoperation of the at least one source to achieve less than 180 degreecoverage by X-rays passing through at least one point of interest to beimaged. 42-44. (canceled)
 45. A method of manufacturing an apparatus,wherein the method comprises: integrating a table on which a patient maybe placed with at least one X-ray source configured to generate X-raysat a plurality of X-ray source locations along a linear direction,wherein the at least one X-ray source is arranged to generate the X-rayssuch that at least some of the X-rays pass through at least a portion ofthe table in addition to passing through a patient placed on the table,wherein the apparatus further comprises at least one detector arraycomprising a plurality of detector elements and arranged to detect theat least some of the X-rays passed through the portion of the patientplaced on the table, wherein the at least one detector array comprisesdetector elements arranged in a two-dimensional configuration. 46-49.(canceled)
 50. The method of claim 45, further comprising mounting theat least one X-ray source substantially below the table.
 51. The methodof claim 50, further comprising positioning the at least one X-raysource such that the at least one X-ray source includes a portion thatextends at least partially above the table.
 52. (canceled)
 53. Themethod of claim 45, further comprising mounting the at least one X-raysource substantially above the table.
 54. The method of claim 45,wherein the at least one X-ray source is configured to be stationaryduring a single acquisition of data used to reconstruct an image. 55.The method of claim 45, further comprising mounting the at least oneX-ray source such that the at least one X-ray source is translatablealong a length direction and/or a width direction of the table. 56-79.(canceled)
 80. The method of claim 45, wherein the apparatus furthercomprises: read-out circuitry configured to read out information fromone or more detector elements of the at least one detector array,wherein the read-out circuitry is configured to provide the informationread out from the one or more detector elements to at least oneprocessor programmed to perform a volumetric image reconstruction.81-99. (canceled)
 100. A non-transitory computer readable medium encodedwith a plurality of instructions that, when executed by at least onecomputer processor perform a method comprising: receiving X-ray datafrom at least one detector array, wherein the received X-ray data doesnot satisfy a volumetric reconstruction requirement; and reconstructing,with the at least one computer processor, the volumetric image using aniterative reconstruction technique based, at least in part, on thereceived data.
 101. The non-transitory computer readable medium of claim100, wherein reconstructing the volumetric image comprisesreconstructing the volumetric image using an iterative reconstructiontechnique selected from the group consisting of OSIRT, SART, SIRT, OSC,C, SMART, MART, and EM.
 102. The non-transitory computer readable mediumof claim 100, wherein reconstructing the volumetric image comprisesreconstructing the volumetric image using a regulator.
 103. (canceled)104. (canceled)
 105. The non-transitory computer readable medium ofclaim 100, wherein reconstructing the volumetric image comprisesreconstructing the volumetric image based, at least in part, on priorsdetermined using a plurality of images from a plurality of patientsand/or priors determined using at least one whole-image statistic.106-109. (canceled)
 110. The non-transitory computer readable medium ofclaim 100, wherein the volumetric reconstruction requirement is arequirement selected from the group consisting of a Tuy condition, api-line-condition, a Nyquist condition, and a non-truncation condition.